Adjustable drain plate in a paper web forming zone

ABSTRACT

A mechanism and method for forming a web from a fibrous stock slurry with a traveling fourdrinier wire for receiving a slurry from a headbox having upper and lower slice lips in close proximity to the wire with the upper lip on a pivotal forming roof which is pivoted on another portion of the roof to provide an adjustable throat and a plate adjustable in the machine direction beneath the wire and movable across the slice opening to control the length of the drainage zone and the location of the dry line on the wire.

United States Patent [1 1 Bringman Sept. 23, 1975 1 1 ADJUSTABLE DRAINPLATE IN A PAPER WEB FORMING ZONE [75] Inventor: David J. Bringman,Beloit, Wis.

[73] Assignee: Beloit Corporation, Beloit, Wis.

[22] Filed: Dec. 24, 1974 [21] Appl. No.: 536,233

Related U.S. Application Data [63] Continuation of Ser. No. 345.324,March 27. 1973,

3.190.790 6/1965 Ploetz et a1. 162/212 3.3571180 12/1967 Curtis 1.162/350 X 3,676,294 7/1972 Opderbeck ct a1; 1. 162/350 X 3,764,46510/1973 Bartley et al. i v. 162/351 3,775,244 11/1973 Hubschmann 162/351Primary ExaminerS. Leon Bashore Assistant Examiner-Richard V. FisherAttorney, Agent, or FirmHill, Gross. Simpson, Van Santen, Steadman,Chiara & Simpson [5 7] ABSTRACT A mechanism and method for forming a webfrom a fibrous stock slurry with a traveling fourdrinier wire forreceiving a slurry from a headbox having upper and lower slice lips inclose proximity to the wire with the upper lip on a pivotal forming roofwhich is pivoted on another portion of the roof to provide an adjustable throat and a plate adjustable in the machine direction beneaththe wire and movable across the slice opening to control the length ofthe drainage zone and the location of the dry line on the wire.

9 Claims, 2 Drawing Figures US Patent Sept. 23,1975

02 Y L //VE ADJUSTABLE DRAIN PLATE IN A PAPER WEB FORMING ZONE This is acontinuation of application Ser. No. 345,324, filed Mar. 27, 1973, nowabandoned.

BACKGROUND OF THE INVENTION The present invention relates toimprovements in methods and mechanisms for the continuous pressureforming of nonwoven synthetic webs or paper webs or a combinationthereof, and particularly to an arrangement for controlling the rate ofwater tain an improved web. 7

In the formation of a web a fibrous slurry of stock is pressuredischarged onto a traveling wirefrom a headbox having a slice openingexposed to the wire for a distance. Beyond the headbox a dry lineappears on the wire to indicate the end of the drainage zone. As isrecognized by paper makers, the dry line is a phenomena which provides avisible line across the forming wire that enables the paper maker toadjust the machine for uniform basis weight across the machine width.

A feature of the invention is to provide a pressure full hydraulicheadbox which is positioned to'be angled upwardly to prevent theformation of air pockets in the flowing stock. A further feature of theinvention is the provision of an upwardly inclined-traveling wirereceiving the stock from the slice opening with the headbox having aforming roof over the forming zone of the wire.

In forming the web with cellulose or synthetic fibers with a pressureheadbox and a roof extending over the drainage zone, it has beendiscovered thatin this type of structure for optimum formation it isimperative that free water is discharged from the distal edge of theupper slice lip to the extent that the gap between the forming wire andthe slice lip is fully occupied by the partially formed web and water.It is also desirable to maintain the free water discharge from the slicetip at a minimum in order to effect a dry line or formed sheet as soonafter the slice discharge as feasible. Excess free water discharge fromthe slice can effect poor formation partly due to the tendency of thewater to adhere upwardly toward the slice tip while the partial formedweb adheres to the forming wire traveling therebe neath. This creates avoid or air entrainment between the free water and partially formed web.

The upwardly traveling forming wire must be maintained at an angle whichis critical in that it is desirable to maintain an upward flow throughthe headbox inlet, body and slice to avoid the creation of air pockets.A horizontal or level wire system would be feasible if an air bleedarrangement is utilized at the high point of the headbox system.

It has been discovered that factors affecting the amount of free waterdischarge from the slice of the forming roof are: i t

1. Slice opening.

2. Stock consistency and freeness.

3. Pressure differential across the wire which is dependent upon thestock head and drainage device vacuum beneath the wire.

4. Resistance to flow of water through the forming wire.

5. Resistance of flow of water through the'partially formed mat or web.

6. Stock temperature,- viseosity and other factors affecting flow.

drainage to ob- 7. Drainage area or drainage zone length.

ln-the formation of nonwoven webs wherein synthetic fibers are used andin the formation of free draining cellulose fiber blends and on certainpaper grades, it is desirable to operate the headbox for inlet waterrates over a large range of volumes. This range can vary from 2 to l onpaper grades up to 10 to l or higher for nonwoven grades containing atleast a portion of synthetic fibers. In the manufacture of nonwoven websby web processes, the entering stock consistency requirement andresulting water rate is largely dependent on fiber length. The longerthe fiber, the lower the consistency, or in other words, the higher thewater rate required. Water rate requirements and resulting drainagerequirements will vary for nonwoven webs with fiber length and will varywith paper or paper combined with nonwoven blends with fibercharacteristics, stock freeness, stock consistency, and change in basisweights and machine speeds.

In the wet process manufacture of paper or nonwoven webs or blendsthereof, as stated, it is important to maintain a minimum of free waterdischarge from the roof slice tip and it is important to control thewater rate through the headbox and onto the forming wire for variousfurnishes, basis weights and machine speeds. The drainage rate throughthe forming wire must also be variable in direct proportion to theheadbox flow rates. It isalso desirable that the drainage rate change becontrollable in a short time, preferably during operation of themachine. One method of varying the drainage rate is by changing thepressure differential across the web by change of vacuum in the vacuumbox or drainagedevice beneath the wire. Some control can be obtained bythis means, but sufficient changes in drainage cannot be obtained solelyby this means to match headbox water rate changes, particularly withfree draining cellulose stocks and synthetic fiber furnishes of lowconsistency. Sufficient control also cannot be obtained over moderate toextreme basis weight changes.(at constantspeed) or speed changes (atconstant basis weight). Also, sufficient control cannot be maintainedwith changes in speed and basis weight that simultaneously increase ordecrease water rate requirements.

It is accordingly a. feature of the present invention to provide amethod and mechanism of varying the drainage rate through a continuoustraveling forming wire when delivering the stock to the forming wireunder a forming roof such that pressure formation will be utilized. Theinvention embodies a drainage device plate or cover and a supportingmember incorporating a vacuum box with compartmented drop legs forvacuum retention and connection for vacuum pumps. The drainage devicecover or plate is adjustable in position in the machine direction tovary the effect of slice opening and to vary the length of the drainagezone. This arrangement allows for infinite adjustment within the maximumouter limits of the slice opening, i.e., drainage area.

It is accordingly an object of the present invention to provide animproved pressure forming arrangement wherein the water drainage can bereadily controlled during operation so that a wide variety of operatingconditions can be accommodated.

A further object of the present invention is to provide an improvedpressure formation structure for forming a traveling web from a stockslurry wherein various flow factors through the headbox can be changedfor optimum web formation and the water drainage independentlycontrolled by an improved arrangement for varying the water drainedthrough the forming surface.

Other objects, advantages and features, as well as equivalents thereofwhich are intended to be covered herein, will become more apparent withthe teaching of the principles of the invention in connection with thedisclosure of the preferred embodiments in the specification, claims,and drawings, in which:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view shownschematically, partially in section, of an arrangement constructed andoperated in accordance with the principles of the present invention; and

FIG. 2 is a similar side elevational view showing the parts adjusted toanother position.

DESCRIPTION As shown in FIGS. 1 and 2, the mechanism includes apressurized stock supply inlet leading to a pressure headbox 11 whichextends in an upwardly inclined direction so as to avoid the formationof air bubbles in the flowing stock. The stock is deposited on atraveling forming surface in the form of a fourdrinier wire 12 whichextends in an upwardly inclined direction in the forming run with theinclined direction being provided so as to accommodate the upwardinclination of the headbox. The wire is supported on suitable rollsincluding a breast roll 13.

The headbox has a slice opening 14 where the stock is exposed to thetraveling wire to provide a pressure formation slice opening. The sliceopening extends from the distal edge of the lower slice lip 15 to thedistal edge of the upper slice lip 17. The upper slice lip is at theedge of the upper forming roof 16 which is pivotally mounted on theheadbox at a pivot point 18. Power means such as jack screws shownschematically at 22 are provided for moving the forming roof up or downto control the space between the slice lip 17 and the wire 12.

The forming roof 16 is supported on a roof extension 19 which is part ofthe top of the headbox and which is pivoted at 20. By moving the roofextension 19 up or down, the size of the throat of the headbox leadingto the slice chamber can be adjusted, and this is accomplished by powermeans shown schematically at 21 which may be in the form of jack screwsor similar power adjustment members.

Beneath the wire is a suction box means 23 divided into compartments23a, 23b. 23c and 23d. Beneath the wire at the topv of the suction boxis a box top 29 which has suitable large openings for the water tofreely pass through the wire and into the suction box. The suction boxleads downwardly into a water collection container A suction pump 25 hasa suction line 25a connected to the various compartments which may haveindividual valve controls so as to control the vacuum in each of thecompartments. A normally increased vacuum will be applied in eachsuccessive compartment as the .thickness of the web builds up on thewire.

At the upstream end of the slice opening is a drainage plate or cover 26which is adjustably movable across the slice opening to block drainage.The plate 26 is shown in the maximum open position in FIG. 1 and in themaximum closed position in FIG. 2. Power means I shown schematically at27 are provided for moving this drainage blocking plate to the desiredadjusted position. The plate is secured to the suction box 23 which 5 isalso movable and a power means 28 will be provided which may be part ofthe power means 27 for shifting the box 23 and the plate 26 in themachine direction. Drainage will begin at the downstream edge of theplate 26 and the distance from this edge to the upper slice lip is theforming zone length. i

Following the downstream upper slice lip 17 a dry line 15a will appear.In accordance with the principles of the invention, the plate 26 will beadjusted in a positionrelative to the other factors of machine operationso as to maintain the dry line one-eighth to 5 inches beyond the upperslice lip 17, and preferably one-half to 3 inches.

Thus, a drainage zone will be formed. which will extend from thedownstream edge 26a of the plate 26 to the dry line 15a the drainagedistance being shown by the arrowed line 30 in FIG. 1, and by 30' inFIG. 2. The upper slice lip 17 will be positioned so that a minimum of.free water discharge from the roof past the slice lip will occur. Theposition of the plate will be set relative to the headbox flow rate sothat the dry line occurs at the location above discussed, i.e.,immediately downstream of the upper slice lip. The drainage rate must becontrolled to match headbox water rate changes and absolute control isessential with free draining cellulose stocks and synthetic fiberfurnishes of low consistency.

I claim as my invention:

l. The method of forming a web from a fibrous stock slurry with amechanism' having a movable porous forming surface for receiving aslurry of stock and draining water therefrom to form a traveling web,the headbox having upper and lower slice lips in close proximity to theforming surface with the distance from the lower to the upper slice lipdefining a machine direction slice opening along the forming surface andthe 0 machine direction distance from the location where the waterbegins draining from the stock to the dry line defining a drainage zone,and having a drain plate means with an imperforate portion and aperforate portion opposite the slice opening with the imperforateportion blocking the slice opening to prevent flow through the formingsurface with the imperforate portion being of v sufficient length toblock the drainage zone for substantial lengths, the method includingthe steps of detera substantial distance beyond the lower slice lip tocontrol the length of the drainage zone by moving the plate I to changethe distance the imperforate portion extends in the machine direction toblock controlled lengths of the slice opening to position the dry line apredetermined distance beyond the upper slice lip.

2. The method in accordance with claim 1 wherein: the upper slice lip isadjustable relative to the forming surface to control free water passingthe upper slice lip. 3. The method in accordance with claim 1 wherein:the dry line is adjusted to extend one-eighth to 5 inches beyond theupper slice lip. 4. A mechanism for forming a web from a fibrous stockslurry comprising in combination:

a movable porous forming surface for receiving a slurry of stock anddraining water therefrom to form a traveling web;

mining the dry line by blocking the forming surface for a headbox havinga lower slice lip in close proximity 5. A mechanism for forming a webfrom a fibrous to the forming surface and having a roof extending stockslurry constructed in accordance with claim 4, over the forming surfacewith an upper slicc lip in including a suction box positioned beneaththe form close proximity thereto, the distance from the ing surface withmeans to control the vacuum in lower to the upper slice lip defining amachine di- 5 said suction box. rection slice opening along the formingsurface. a 6. A- mechanism for forming a web from a fibrous dry lineappearing along the web on the forming stock slurry constructed inaccordance with claim 4, surface downstream from the upper slice lip;wherein said headbox is angularly inclined upwardly. drain plate meansextending beneath the forming sur- 7. A mechanism for forming a web froma fibrous face opposite the slice opening, said drain plate 10 stockslurry constructed in accordance with claim 4: means having animperforate portion and a perfowherein said forming surface is atraveling wire. rate portion downstream therefrom relative to the 8. Amechanism for forming a web from a fibrous direction of forming surfacetravel, said imperforstock slurry constructed in accordance with claim4: ate portion blocking drainage through the forming wherein saidheadbox has a forming roof extending surface and being of sufficientlength to block the angularly upwardly above the wire and said roofdrainage area for substantial lengths with machine being pivotal at itsupstream edge to vary the disdirection movement of the plate means;tance between the upper slice lip and the wire. and means for movingsaid drain plate means in the 9. A mechanism for forming a web from afibrous machine direction to increase the imperforate area stock slurryconstructed in accordance with claim 8: and decrease the perforate areaopposite the slice wherein said forming roof is hinged on a pivotalopening to controllably vary the length of time of headbox roof portionwhich is adjustable to vary drainage beneath the upper slice lip wherebythe the size of a portion of the headbox leading to the plate can beadjusted to be a predetermined disslicc opening. tancc beyond the slicelip.

1. THE METHOD OF FORMING A WEB FROM A FIBROUS STOCK SLURRY WITH AMECHANISM HAVING A MOVABLE POROUS FORMING SURFACE FOR RECEIVING A SLURRYOF STOCK AND DRAINING WATER THEREFROM TO FORM A TRAVELLING WEB, THEHEADBOX HAVING UPPER AND LOWER SLICE LIPS IN CLOSE PROXIMITY TO THEFORMING SURFACE WITH THE DISTANCE FROM THE LOWER TO THE UPPER SLICE LIPDEFINING A MACHINE DIRECTION SLICE OPENING ALONG THE FORMING SURFACE ANDTHE MACHINE DIRECTION DISTANCE FROM THE LOCATION WHERE THE WATER BEINGSDRAINING FROM THE STOCK TO THE DRY LINE DEFINING A DRAINAGE ZONE, ANDHVING A DRAIN PLATE MEANS WITH AN IMPERFORATE PORTION AND A PERFORATEPORTION OPPOSITE THE SLICE OPENING WITH THE IMPERFORATE PORTION BLOCKINGTHE SLICE OPENING TO PREVENT FLOW THROUGH THE FORMING SURFACE WITH THEIMPERFORATE PORTION BEING OF SUFFICIENT LENGTH TO BLOCK THE DRAINAGEZONE FOR SUBSTANTIAL LENGTHS, THE METHOD INCLUDING THE STEPS OFDETERMINING THE DRY LINE BY BLOCKING THE FORMING SURFACE FOR ASUBSTANTIAL DISTANCE BEYOND THE LOWER SLICE LIP TO CONTROL THE LENGTH OFTHE DRAINAGE ZONE BY MOVING THE PLATE TO CHANGE THE DISTANCE THEIMPERFORATE PORTION EXTENDS IN THE MACHINE DIRECTION TO BLOCK CONTROLLEDLENTHS OF THE SLICE OPENING TO POSITION THE DRY LINE A PREDETERMINEDDISTANCE BEYOND THE UPPER SLICE LIIP.
 2. The method in accordance withclaim 1 wherein: the upper slice lip is adjustable relative to theforming surface to control free water passing the upper slice lip. 3.The method in accordance with claim 1 wherein: the dry line is adjustedto extend one-eighth to 5 inches beyond the upper slice lip.
 4. Amechanism for forming a web from a fibrous stock slurry comprising incombination: a movable porous forming surface for receiving a slurry ofstock and draining water therefrom to form a traveling web; a headboxhaving a lower slice lip in close proximity to the forming surface andhaving a roof extending over the forming surface with an upper slice lipin close proximity thereto, the distance from the lower to the upperslice lip defining a machine direction slice opening along the formingsurface, a dry line appearing along the web on the forming surfacedownstream from the upper slice lip; drain plate means extending beneaththe forming surface opposite the slice opening, said drain plate meanshaving an imperforate portion and a perforate portion downstreamtherefrom relative to the direction of forming surface travel, saidimperforate portion blocking drainage through the forming surface andbeing of sufficient length to block the drainage area for substantiallengths with machine direction movement of the plate means; and meansfor moving said drain plate means in the machine direction to increasethe imperforate area and decrease the perforate area opposite the sliceopening to controllably vary the length of time of drainage beneath theupper slice lip whereby the plate can be adjusted to be a predetermineddistance beyond the slice lip.
 5. A mechanism for forming a web from afibrous stock slurry constructed in accordance with claim 4, including asuction box positioned beneath the forming surface with means to controlthe vacuum in said suction box.
 6. A mechanism for forming a web from afibrous stock slurry constructed in accordance with claim 4, whereinsaid headbox is angularly inclined upwardly.
 7. A mechanism for forminga web from a fibrous stock slurry constructed in accordance with claim4: wherein said forming surface is a traveling wire.
 8. A mechanism forforming a web from a fibrous stock slurry constructed in accordance withclaim 4: wherein said headbox has a forming roof extending angularlyupwardly above the wire and said roof being pivotal at its upstream edgeto vary the distance between the upper slice lip and the wire.
 9. Amechanism for forming a web from a fibrous stock slurry constructed inaccordance with claim 8: wherein said forming roof is hinged on apivotal headbox roof portion which is adjustable to vary the size of aportion of the headbox leading to the slice opening.